This is the rev limiter kicking on. 4 mix Stihls run a lot less RPM's than a traditional 2 cycle. They do have a tremendous torque band and power through thick or heavy weeds really well. I ran FS80's for years and when Stihl dropped it, I switched to RedMax. We run the BCZ2460 and really like them. I just don't like the 4 mix.

I took the plunge and bought my first Stihl trimmer. Very different beast from the Redmax trimmers I've been using. I have run 5 tanks of quality fuel with Stilhl HP oil and I have a concern regarding the smoothness of engine. 3/4 throttle and the unit runs nice and smooth, but full throttle and the engine housing starts shaking violently and sounds like it's missing. Full throttle in heavy growth it runs fine, but when it's only light trimming duty it starts acting up. I also switched to some .105 line and that seemed like it added enough load to smooth it out some at full throttle. I took it back to the dealer to have them look at it and 2 minutes later they brought it back and said all is fine. I've also noticed that it will stumble for a split second when testing from various throttle positions to WOT. This is the first 4mix tool I've laid my hands on, so really not sure if it's truly and issue or not.

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Wellcome to 4 mix. We got 4 shindawa units and I hate that little hesitation. We are in the third year with the units and I noticed yesterday all 4 are in the shop ready to go but none of the worker select them when given other choices....i.e. 2 stroke echo 265T. The place that it kills you is when usingit as a trimmer and you are trying to feather the throttle. Now I see why all these stihl guys get edgers. We will not buy any more unless the 2 stroke is killed off.

Thanks for the replies and it's good to know that nothing is wrong, sort of. I guess it's just part of the learning process of the little nuances of a new trimmer. I love my Redmax trimmers, but wanted to try Stihl this time mainly due to the dealer network like so many others have commented. Regarding the valve adjustment, I'm assuming Stihl considers that a dealer only adjustment. I didn't see the procedure in the operators manual.

we are phasing out of the stihl 4 mix...they cost considerably more to own than some of the other brands and we dont seem to get the life out of them even if they are maintained properly....everything seems over engineered and over priced on them...my guys are always grabbing the echo's or shindiawas over the stihls....they are smoother, better balanced, better on fuel and cost less to maintain/repair....that said the stihls do have more power though...but unless youre always doing clean ups its overkill....

I dont see why everyone bashes Stihl. I run a Fs90R trimmer and a Br500 Backpack blower and I love them. Never had any problems out of them beside changing air filters. When I run my trimmer short on string I notice that it revs up harder like it wants to blow up. I also run without the guard so I run more string than what the shield will allow but I like it. It keeps the power right where I want it with the load. I normally only run half throttle with it too unless I get into thick stuff but for all my weekly and biweekly I run at half throttle. And I will say I actually get done quicker using the Stihl trimmer than I do with other brands I have tried.

I dont see why everyone bashes Stihl. I run a Fs90R trimmer and a Br500 Backpack blower and I love them. Never had any problems out of them beside changing air filters. When I run my trimmer short on string I notice that it revs up harder like it wants to blow up. I also run without the guard so I run more string than what the shield will allow but I like it. It keeps the power right where I want it with the load. I normally only run half throttle with it too unless I get into thick stuff but for all my weekly and biweekly I run at half throttle. And I will say I actually get done quicker using the Stihl trimmer than I do with other brands I have tried.

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We aren't bashing anything except the 4 mix and its little problem of low end acceleration and the annoying start up delay. Oh and if you ever do have any problems with those units look out.....you obviously haven't looked into replacing seal and bearings on units.

Regarding the valve adjustment, I'm assuming Stihl considers that a dealer only adjustment. I didn't see the procedure in the operators manual.

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The valves being out of adjustment often cause problems like hard starting and slow to rev. I adjust mine once a year whether I have a symptom or not. Usually one or both valves need a small adjustment. I just did 2 4 Mix engine valve adjustments this past Sunday and it took about 45 minutes total for both of them. The adjustment is super easy and the only special tool you need is the special feeler gauge that you can buy from your dealer. Here's a video from Stihl that shows how to do it.